Supply circuits for thermionic tubes



Aug" 7, 1934. A. H. COOPER 1,968,375

' SUPPLY CIRCU ITS FOR THERMIONIC TUBES Filed May 9, 1931 INVENTOR.

11/ ATTORNEY.

Patented 'Aug. 7, 1934 PATENT OFF'I 1,968,875 h SUPPLY cmcm'rs FORTHERMIONIC TUBES Arthur Henry Cooper Appledore, .Syke I ngs, Iver,

England, assignor to Electric and Musical Industries Limited, Middlesex,England, a company of Great Britain Application May 9, 1931, Serial No.536,278 In Great Britain May 20, 1930 15 Claims. (c1. 25o--z7) Thisinvention relates to' means for supplying grid bias voltages'tothermionic devices which are required to operate from alternatingcurrent supply mains.

Hitherto, where the grid bias voltage has been derived from alternatingcurrent supply mains, one or other of the two following methods hasusually been employed for obtaining the required potential. I

In one known method, a series resistance has been inserted in thenegative high tension supply to one or more of the tubes, and thevoltage drop along this resistance has been used to provide the gridbias. This method is open to objection for two reasons. Firstly, thehigh tension current of the last, and usually the largest tube must flowthrough this resistance and the energy thereby dissipatedmay amount to aquarter of the total energy consumption. Secondly, since the fluctuatingcurrent of the last tube is employed to provide a potential for thepreceding grids, reaction is liable to be set up, and this mustbeprevented by additional apparatus entailing fur ther expense.

In another known method, a rectifying unit, entirely separate from thatemployed for supplying the anode potential, has been provided forsupplying the'grid bias voltage. This method overcomes the disadvantagesmentioned in the preceding paragraph but only at a considerablygreatercost. V

An object of this invention is to provide an inexpensive and reliablemeans for obtaining, from an alternating current supply, the gridpotentialfor thermionic tubes; I

A further object of this. invention is to provide an inexpensive andreliable means for obtaininga main 3 supply of unidirectional potentialfor a portion of thermionic tube apparatus, and one or more separatesupplies of unidirectional potential for other portions,respectivelygof. such apparatus, deriving said supplies from a commonalternating current secondary winding], of a power transformer bymeansjflof separate rectifiers and filters. Accordin tothis invention,in thermionic tube apparatus ijrl'which anode and grid bias potentialsare derived from an alternating current source, the anodepotential foratube being obtained from .the seeondarywindingof atransformer with theaid ofa rectifienth'ere are provided means whereby the grid bias,voltage for the same tube is obtained from the same secondary windingwith the aid. of a separate rectifier. 1 h

Other objects of my invention will become evident from the followingdetailed description taken.

inconjunctionwith the accompanying drawing, in which in i i Fig. 1 thereis illustrated diagrammatically a preferred method of carrying theinvention into effect, and

Fig. 2 is a circuit diagram of a specific form of my invention. 7

Referring to the drawing, in Fig. 1 the two anodes of a full waverectifying valve 1, hereinafter termed the main rectifier, are connectedacross the secondary winding 2 of a transformer, the primary winding ofwhich is adapted to be supplied with energy from an alternating currentsource such, for example, as the electric supply mains; The current forheating the filament of the rectifier 1 is also derived from the samesource of alternating current by means of a separate winding 3 on thetransformer. The positive lead from the filament of the main rectifier 1is connected through-a suitable smoothing circuit or filter comprising achoke 4 in series andcondensers 5 and '6 in shunt, to the anode circuitof a thermionic tube apparatus of which only one tube? is shown inFig. 1. The negative lead 20 from the rectifier 1 is taken from themiddle point of winding 2 and is connected to the middle point of afurther secondary winding 8 on the transformer.

This winding 8 is adapted to supply the current for heating thefilaments of the thermionic tube apparatus and, in addition, thefilament of a second full wave rectifying valve 9 from which the gridbiasin potential is to be derived. The rectifier 9, which may be of asmall inexpensive single wave type, is adapted to be supplied withcurrent from the same secondary winding 2 which supplies therectifier 1. The anodes are connected through high impedances lo and10', which maybe resistors or condensers, to the ends of theWlndingzandthe filament to the middle point of the same winding. Forpurposes of illustration impedances 10 and 10 have been'shown ascondensers in Fig. 1-. The output from the rectifier 9is passed onto thenegative side 20 of the circuit through high resistance or reactanceelements 11 and 11 to one terminal of a potentiometer 12 shunted by asmoothing condenser 13.

The-positive leadfrom the rectifier 9 is connected to the other terminalof the potentiometer 12.

The grid bias for the tube 7r is obtained from 'the rectifier 9 "throughlead 14, and the grid bias of other stages isderived through leads 15and 16 fromtappings taken on the potentiometer 12.

' As thejcurrent'which is derived from the windinglisusually at a highpotential and there is,

of each of the rectifiers l and-9,;and' when alternating current ispassed through the primary winding of the transformer, rectified currentfor the anode circuit of the thermionic tube '7 and associated tubes isobtained from the rectifier 1, v

and the grid bias potential is obtained from the rectifier 9 and tappedofi from the potentiometer 12' It will be clear that the current forheating the filaments of the rectifier 9 and thermionic tubes 7 may, ifdesired, be derived from a'separa'te source such, for example, as abattery and not from the secondary winding 8 of the transformer,Further, instead of connecting the filamentof the grid bias rectifier 9in parallel with the filaments of the thermionic valve apparatus, therectifier filament can, if desired, be connected in series thereto.

For purposes of illustrating some of the above mentioned modifications Ihave shown in simplified rearranged form in Fig. 2 a diagram of a halfwave bias valve 9" supplied with current from the secondary winding 2.The mainsystem may similarly employ half wave rectification, but forreasons well known the double wave arrangement shown is preferred. Thevalve 9 maybe conveniently connected to an end of the winding as bymeans of a resistor 10 of suitable value to reduce the voltage appliedto the bias valve, substantially the same as if the valve were connectedto an additional intermediate tap on the secondary 2. The resistanceelements 10, 11 and 12 may obviously, if desired in practice,be in thephysical form of a unitary high resistance or impedance element tappedat the desired points, the valve 9' being in shunt with portions 11 and12. The resistance element 11, which may possess inductive reactance,constitutes with the condenser 13 an efiective filter section forreduction through the bias resistor 12 by inverting the bias rectifierin order to provide a positivesource of bias potential if desired.

In the above systems the biasrectifier has'its anode circuit fed by theusual high voltage Winding of the main rectifying system, and its-fi131,

ment energized by one of the usual filament windings for the radioapparatus, with a consequent I saving in expense and with thepossibility of adapting existing apparatus to my improved system.However, it is sometimes desirable vto use another filament winding forthe bias valve, separate from the winding 8, e. g. in case the currentand voltage ratings of. the filaments are difierent. r i

A reason for connecting the bias rectifier or valve in shunt relationwith the load,.or resistors 11 and 12, as above shown, has to .do withthe fact that the same filament winding 8-.is'used for both the biasvalve and the radio apparatus. It is obvious, however, to one skilled inthe art that if a separate filament winding is used for the bias valvethe latter may be connected in series with its load in the conventionalmanner, as in the case of the main rectifier 1, and the valve maylikewise be connected directly to a high potential end of the winding.Although a filament type of bias valve has been shown, any othersuitable type of well known rectifier or converter could be used, and ifdesired two separate single wave valves may obviously be used in placeof the main full wave rectifier valve 1.

Having now particularly described and ascertained the nature of my saidinvention, and in what manner the same is to be performed, I declarethat what I claim is:

1. In combination with thermionic tube apparatus, an alternating currentsupply winding, means connected with one end of said Winding forsupplying a portion of said thermionic apparatus with rectifiedpotential of positive polarity relative to a point of referencepotential, and means connected to the other end of said winding forsupplying unidirectional potential of negative polarity relative to saidpoint to another portionof saidthermionic apparatus, said point beingconnected to said winding intermediate the ends thereof. I

2. In combination with thermionic tube apparatus, an alternating currentsupply winding,

converting means connected in series with said winding between spacedpoints for supplying a portion of said thermionic apparatus withcurrent, and a second converting means connected in shunt .relation withsaid winding between other spaced points thereon for supplyingunidirectional potential to another portion of said thermionicapparatus.

3. In combination, thermionic tube apparatus, an alternating currentsupply winding, a rectifier connected to said winding for supplyinganode voltage to the tubes in said apparatus, an impedance networkincluding inductive reactance means connected across a portion of saidwinding, and a second rectifier connected to said network for providinggrid bias potentials for said thermionic tube apparatus, the connectionsbeing such that alternating potential is supplied to each rectifier inphase. 4. In a supply circuit for thermionic tube apparatus, means forsupplying plate potential to said apparatus comprising a rectifier and amidpointof high potential on said transformer secondarywinding withrespect to the mid-point thereof.

5. In a supply circuit for thermionic tube apparatus, means forsupplying plate potential to said apparatus comprising a rectifier and asecondary winding of a transformer connected to a source of alternatingcurrent, means for supplying grid bias potential to said apparatuscomprising a second rectifier, a. high impedance element for connectingan electrode of said second rectifier to a high potential point on said1 transformer secondary,-a potentiometer connecton said winding, andmeans for connecting a control electrode of said apparatus to a point onsaid potentiometer.

6. In a supply circuit for thermionic tube apparatus, means forsupplying plate potential to said tube apparatus comprising a rectifierand a. secondary winding of a transformer connected to a source ofalternating current, means for supplying grid bias potential to saidthermionic apparatus comprising a second rectifier, an impedance elementconnecting the anode of said second rectifier to a high potential pointon said secondary winding and a resistor connected between saidrectifier anode and an intermediate point of lower potential on saidwinding for deriving said grid potential.

7. In a power supply system for thermionic apparatus comprising amiddle-tapped alternating current supply winding, a full wave rectifierconnected with said winding for supplying a portion of said thermionicapparatus with current, a sec ond rectifier of the half wave typeconnected with one of the half portions of said winding for supplyingunidirectional potential to another portion of said thermionicapparatus.

8. In a power supply system forthermiom'c tube apparatus, means forsupplying anode potential to said apparatus comprising a double waverectifier and associated alternating current supply winding, means forsupplying grid potential to said thermionic apparatus comprising a highimpedance network connected in shunt with a half of said winding, asecond rectifier connected in shunt with a portion of said network, andmeans for filtering the rectified current from said second rectifier.

9. In a supply circuit for thermionic tube apparatus, means forsupplying plate potential to said tube apparatus comprising a rectifierand a secondary winding of a transformer connected to a source ofalternating current, means for supplying grid bias potential to saidthermionic apparatus comprising a second rectifier associated with saidsecondary winding, a condenser for connecting said rectifier to a highpotential point on said secondary winding and a filter network connectedbetween said rectifier and a point of lower potential on said secondaryfor smoothing out the resultant rectified current.

10. In a supply circuit for thermionic tube apparatus, means forsupplying plate potential to said tube apparatus comprising analternating current supply winding, means for supplying grid potentialto said apparatus comprising an impedance network connected across aportion of said winding, a rectifier having its anode connected to arelatively high potential point on said network and its cathode to a lowpotential point on said network, means connected with a portion of saidnetwork for deriving said grid potential.

11. In a supply circuit for thermionic tube apparatus, means forsupplying plate potential to said tube apparatus comprising a rectifierand a secondary winding of a transformer connected to a source ofalternating current, means for supplying grid bias potential to saidthermionic apparatus comprising a second rectifier of the filamentarytype whose anode is connected to a point on said winding, and a separatewinding on said transformer for energizing the filament of said secondrectifier, said separate winding being adapted to supply cathode currentto a tube of said thermionic apparatus.

12'. In combination, a power-transformer having a secondary winding, aplurality of rectifying devices each having an anode and a cathode, onedevice adapted to supply relatively heavy current at high potentials andanother of said devices adapted to supply relatively light currents fromwhich biasing potentials may be derived, and connections for applyingalternating potentials to both of said devices from said secondarywinding, the connections being such that alternating potential issupplied in phase to each device.

13. The invention set forth in claim 12 wherein the cathode of eachdevice is energized from a transformer secondary individual thereto.

14. The invention set forth in claim 12 further characterized in that ananode of the second mentioned device is capacitively connected to ananode of the first mentioned device.

15. The invention set forth in claim 12 characterized in that thecathode of each device is energized from a transformer secondary windingindividual thereto, and additionally characterized in that the cathodeof the second mentioned device is conductively connected to thesecondary winding supplying common anode potentials to the two devices.

ARTHUR HENRY COOPER.

